In the medical field, the infectious disease caused while a medical device formed of a polymeric material such as polyurethane is kept inserted or self-retained in the body of a patient is considered a problem as one of complications. Hitherto, in order to prevent the infectious disease caused by an indwelling medical device, the medical device is immersed in an aqueous solution containing an antimicrobial agent or disinfectant such as chlorohexidine or povidone iodine for disinfection immediately before use. As another method, in the case where the medical device can be exchanged during treatment, it is frequently exchanged. However, it is evident that an antimicrobial agent or disinfectant vanishes from the surface of a catheter with the lapse of time and cannot sustain the effect of disinfection and that in the case where a medical device is used for a long period of time, the effect of disinfection gradually declines. Further, the frequent exchanges of medical devices impose large burdens on medical workers. Therefore, as means for further prevention of infection, medical devices are variously processed to be antimicrobial. Typical approaches include catheters covered on the surfaces with antimicrobial agents such as chlorohexidine and catheters covered on the surfaces with a layer containing a metal such as silver or copper or a compound thereof. These catheters employ a system in which a material with antimicrobial action is gradually released at a constant rate in the body of a patient, and show a good effect compared with the cases where catheters are disinfected immediately before they are used.
However, a system in which an antimicrobial material is gradually released is still limited in the period of use and cannot avoid that the potency gradually declines. With regard to metals such as silver and compounds thereof, the internal kinetics prevailing after they are gradually released is unknown and they may also be harmful to the human body. Further, in the case where silver remains in the medical device waste after use, any special action of recovering silver from the waste is necessary.
For these reasons, as an alternative to slowly releasable chemicals, various polymers having ammonium groups are proposed as antimicrobial polymers (Patent Document 1). However, these polymers cannot be easily processed and cannot be easily molded alone. Therefore, it is proposed that an article produced by molding a polymer with excellent mechanical properties is coated on the surface with any of such antimicrobial polymers, or that a mixture consisting of an antimicrobial polymer and a polymer with excellent mechanical properties is molded into an article (Patent Documents 2 and 3).
However, a base resin with good mechanical properties, particularly a silicone has a problem that it is poor in adhesion to another polymer, and it is difficult to coat the surface of a silicone with a polymer having ammonium groups. Further, there is another problem that if a polymer containing a siloxanyl structure such as a silicone resin is mixed with a polymer having ammonium groups, transparency is impaired. A material mainly composed of a silicone rubber and capable of gradually releasing an antimicrobial agent is also known, but it does not solve the problem of the aforementioned slow-releasing antimicrobial system (Patent Document 4).
Further, document 5 discloses a method comprising the steps of impregnating a polymer base with a solution of an alkoxysilane with a quaternary ammonium salt and polycondensing said alkoxysilane in such a manner as to form inter-penetrating networks in said polymer base. However, such formation of alkoxysilane condensation product has a problem of raising the elastic modulus of the polymer base, for decreasing the flexibility thereof, and tending to lower the mechanical properties of the polymer base as the case may be.    [Patent Document 1] JP 54-17797 B    [Patent Document 2] JP 10-081717 A    [Patent Document 3] JP 11-99200 A    [Patent Document 4] JP 60-80457 A    [Patent Document 5] JP 2006-509532 A